Form and structure of cell nuclei in growing and hypertrophied human hearts

Tissue portions were taken from eight different places in the right and left ventricle from 17 autopsied human hearts (fetuses, children, adults, hypertrophied and atrophic hearts), and sectioned and smear preparations were obtained and stained after Feulgen. Twenty-eight light microscopic features of heart muscle nuclei were identified, and their percent frequency in individual hearts was obtained.

The studies showed:

• 1.

  Heart muscle nuclei in fetal hearts and in hearts soon after birth show a compact, rounded form in cross section. During childhood heart growth, the nuclei become more and more angular and develop pointed or bizarre projections. In marked heart hypertrophy, almost all heart muscle nuclei assume a bizarre shape and have pointed projections. Compact nuclei are encountered only very occasionally.

• 2.

  In longitudinal section, 80% of heart muscle nuclei in fetal hearts have an oval shape, 20%) are rectangular with rounded corners. During childhood heart growth, the nuclei are angular, and the corners frequently form a point. The smaller edges of the nuclei are cleft. Hypertrophied hearts again show more rounded nuclei.

• 3.

  The external nuclear membrane during childhood heart growth is either smooth or mildly wavy, in contrast to adult heart nuclei which are grooved. Heart hypertrophy again shows predominantly smooth nuclear membranes.

• 4.

  The internal structure of myocardial nuclei (heterochromatin) is granular in the fetal and perinatal periods, whereas it is predominantly netlike in structure during childhood growth phase. Heterochromatin is exclusively coarsely granular in normal, adult hearts, but again finely distributed in a net-like fashion in hypertrophied hearts. Myocardial nuclei from fetuses and children typically show large, round bodies, representing compact DNA aggregates (chromocenters). These are encountered only as isolated findings in normal, adult hearts and in hypertrophied hearts.

• 5.

  The length of heart muscle nuclei remains constant at 9.8 μm during physiologic heart growth, and increases during heart hypertrophy to a mean of 19.2 μm.

• 6.

  Approximately 10% of heart muscle cells from all hearts contain double nuclei and nuclear sequences. The morphological findings of these multinucleate heart muscle cells suggest amitotic nuclear division and nuclear increase.

Shape and structural alterations in heart muscle nuclei permit conclusions to be drawn on the one hand regarding the functional status of the heart muscle, and on the other hand regarding the growth process of the myocardium in physiological heart growth and in pathologic heart hypertrophy. Morphologic evidence is given for amitotic nuclear division as the cause of numerical nuclear hyperplasia in hypertrophied hearts.